The exemplary embodiments described herein relate generally to semiconductor devices and methods for the fabrication thereof and, more specifically, to semiconductor devices having strained PFET and NFET nanosheet structures on the same substrate and methods for forming such structures.
A complementary metal oxide semiconductor device (CMOS) uses pairs of p-type and n-type metal oxide semiconductor field effect transistors (MOSFETs) arranged on silicon or silicon-on-insulator (SOI) substrates. A MOSFET, which is used for amplifying or switching electronic signals for logic functions, has source and drain regions connected by a channel. The source region is a terminal through which current in the form of majority charge carriers enters the channel, and the drain region is a terminal through which current in the form of majority charge carriers leaves the channel. In a p-type MOSFET (hereinafter “PFET”), the majority charge carriers are holes that flow through the channel, and in an n-type MOSFET (hereinafter “NFET”), the majority charge carriers are electrons that flow through the channel. The channel may be defined by an element such as one or more fins, one or more nanowires, or one or more sheets. Such fins, nanowires, or sheets include silicon. One or more gates are positioned over or around the channel to control the flow of current between the source and drain regions.
In devices that employ multiple gates or which use gate-all-around (GAA) technology, the devices benefit from electrostatics and immunity to short channel effects. However, the electron mobility in such multi-gate or GAA devices may be degraded by low-mobility sidewalls and other scattering mechanisms. As a result, strain engineering may be used to improve device performance.
Devices in which GAA nanosheets are employed are attractive candidates for 5 nanometer (nm) technology and beyond due to their excellent electrostatics. In such devices, however, increasing both electron and hole mobility for a CMOS structure may be challenging with regard to suspending nanosheet structures.